Intracavity laser excitation of NCO fluorescence in an atmospheric pressure flame

Abstract

Laser excited fluorescence of the NCO radical has been obtained using discrete prism selected lines of an argon ion laser pump source. To our knowledge this is the first time NCO fluorescence has been obtained in a flame environment. NCO was formed in a slightly rich atmospheric pressure CH4/N2O flame. This flame was placed inside the extended cavity of the argon laser to take advantage of the much higher light intensity levels. All of the available laser lines pump vibrational hot bands of the NCO A 2Σ+ ← X 2Π system. The 4658 Å line appears to be the most useful for probing NCO densities. This line pumps in the A 2Σ+(0,00,0) ← X 2Π (1,01,0) vibrational band. NCO is pumped to N′ = 31 by this line, probably via the Q231 transition although the R230 and P232 transitions could not be ruled out in the present analysis. The 4658 Å line was used to determine a relative NCO density profile through the reaction zone of a CH4/N2O flame. Profiles of C2, CN, and temperature were also obtained in this flame and are compared with the NCO profile. A lower limit of approximately 3×1014 cm−3 was placed on the peak NCO density in the flame. Attempts to find NCO or CN fluorescence in a CH4/air flame failed indicating probable differences in nitrogen chemistry for the two flames.